Intake and exhaust control systems for engine

ABSTRACT

The intake and exhaust control systems are operable in varying modes, according to the engine speed, by a single actuator. The intake control system includes an intake valve that allows a variable amount of air into an air cleaner depending on vehicle speed. The exhaust control system includes an exhaust control valve, and a primary and a secondary exhaust purifying system located downstream of the exhaust control valve. The flow into the exhaust purifying systems may also be controlled according to engine speed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to intake and exhaust control systems foran engine, in which an intake control valve for changing an intake modein accordance with an operational state of an engine is provided in anintake system of the engine, and an exhaust control valve for changingan exhaust mode in accordance with an operational state of the engine isprovided in an exhaust system of the engine.

2. Background Art

A conventional intake control system operates an intake system for anengine and has an intake control valve operated between a first intakecontrol position, at which it gives a low speed side compatible functionto the intake system, and a second intake control position, at which itgives a high speed side compatible function to the intake system. Such aconventional system is disclosed in Japanese Patent Laid-open No. Sho58-155270.

A conventional exhaust control system operates an exhaust system and hasan exhaust control valve operated between a first exhaust controlposition, at which it gives a low speed side compatible function to theexhaust system, and a second exhaust control position, at which it givesa high speed side compatible function to the exhaust system. This typeof conventional system is disclosed in Japanese Patent Publication No.Hei 6-76780.

If the above-described intake control valve and exhaust control valveare provided in an intake system and an exhaust system of the sameengine, the output performance in a wide rotational range of the enginecan be further improved. However, because the control valves areindividually driven by separate actuators, the number of parts isincreased, increasing cost.

A need therefore exists for an intake and an exhaust control systemcapable of improving the performance of the engine in both low and highspeed rotational ranges.

SUMMARY OF THE INVENTION

The present invention overcomes the shortcomings of the conventional artand achieves other advantages not realized by the conventional art.

According to one embodiment of the present invention, intake and exhaustcontrol systems for an engine are provided in which an intake controlvalve for changing an intake mode in accordance with an operationalstate of an engine is provided in an intake system of the engine, and anexhaust control valve for changing an exhaust mode in accordance with anoperational state of the engine is provided in an exhaust system of theengine. The intake control valve and the exhaust control valve aredriven by a common actuator.

According to this aspect of the invention, it is possible to obtain adesired output performance of the engine, irrespective of a change inthe operational state of the engine, by operating the intake controlvalve and the exhaust control valve in accordance with the operationalstate of the engine. The intake valve and the exhaust control valve canbe operated by the common actuator.

Further, since the intake control valve and the exhaust control valveare driven by the common actuator, it is possible to simplify theconfiguration of the drive system, and thereby improve the engineperformance. The cost and weight of the drive system are also reduced.

According to a second aspect of the present invention, the intakecontrol valve is operated between a first intake control position, atwhich the intake control valve gives a low speed side compatiblefunction to the intake system, and a second intake control position, atwhich the intake control valve gives a high speed side compatiblefunction to the intake system. The exhaust control valve is operatedbetween a first exhaust control position, at which the exhaust controlvalve gives a low speed side compatible function to the exhaust system,and a second exhaust control position, at which the exhaust controlvalve gives a high speed side compatible function to the exhaust system.

The first exhaust control position and the second exhaust controlposition of the exhaust control valve are equivalent to a medium speedcontrol position and a high speed control position of a valve body of anexhaust control valve.

According to the second aspect of the invention, since at the low speedrotational range of the engine, the intake control valve, and theexhaust control valve are held at the first intake control position andthe first exhaust control position by the actuator, respectively, it ispossible to give the low speed side compatible function to both theintake system and the exhaust system. This enhances the low speed sideoutput performance of the engine.

When the rotational state of the engine is shifted to the high speedrotational range, since the intake control valve and the exhaust controlvalve are moved to the second intake control position and the secondexhaust control position by the actuator, respectively, it is possibleto give the high speed side compatible function to both the intakesystem and the exhaust system. This enhances the high speed side outputperformance of the engine.

According to a third aspect of the present invention, a lost motionmechanism for absorbing a difference in operational amount between theintake control valve and the exhaust control valve is provided betweenthe actuator and the intake control valve, or between the actuator andthe exhaust control valve. In the third aspect, even when there is alarge difference between the operational amounts of the intake controlvalve and the exhaust control valve, such a difference can be absorbedby the lost motion mechanism, so that both the control valves can becertainly operated by the common actuator.

According to a fourth aspect of the present invention, the exhaustcontrol valve may include a common valve housing interposed on the wayof a first exhaust pipe, and a second exhaust pipe connected tocylinders having differing ignition timing. A valve body is mounted inthe valve housing and switchably turned between a low speed controlposition, a medium speed control position, and a high speed controlposition. At the low speed control position of the valve body, the firstexhaust pipe is communicated to the second exhaust pipe, and the firstexhaust pipe is closed on the downstream side of the communicatedportion. At the medium speed control position, the first exhaust pipeand the second exhaust pipe individually allow exhaust gases to passtherethrough. At the high speed control position, the first exhaust pipeand the second exhaust pipe individually allow exhaust gases to passtherethrough, and an intermediate portion of the first exhaust pipe iscommunicated to an intermediate portion of the second exhaust pipe.

According to the fourth aspect, exhaust gas flowing in the first exhaustpipe is curved, on the way, onto the second exhaust pipe side bycontrolling the valve body at the low speed control position, in orderto increase the exhaust resistance. It is therefore possible to apply anexhaust pressure suitable for the low speed rotational range to theengine, and hence to improve the low speed output performance bysuppressing the blow-by of a new air from each cylinder to the exhaustsystem during the valve overlapping period. The effective pipe length ofeach of the first and second exhaust pipes is set at the maximum lengthmatched to the medium speed operational range of the engine bycontrolling the valve body at the medium speed control position. Thisenhances the volume efficiency by making use of an exhaust inertiaeffect and/or an exhaust pulsation effect, thereby increasing the mediumspeed output performance of the engine. Further, the effective pipelength of each of the first and second exhaust pipes is set at theminimum length matched to the high speed operational range of the engineby controlling the valve body at the high speed control position. Thisenhances the volume efficiency by making use of the exhaust inertiaeffect and/or the exhaust pulsation effect, thereby increasing the highspeed output performance of the engine.

According to a fifth aspect of the present invention, the valve body issupported in the valve housing so as to be turned between the low speedcontrol position, the medium speed control position, and the high speedcontrol position. The valve body has a through-hole crossing the axialline of the valve body, and a communication hole for opening one sidesurface of the through-hole in the radial direction of the valve body.At the low speed control position of the valve body, the communicationhole and the through-hole are concerned with the mutual communication ofthe first exhaust pipe and the second exhaust pipe, and a valve wall,opposed to the communication hole, of the valve body is concerned withthe closing of the downstream side of the first exhaust pipe. At themedium control position, the through-hole is matched to the pipe line ofthe first exhaust pipe, and the valve wall is concerned with theblocking between the first exhaust pipe and the second exhaust pipe. Atthe high speed control position, the through-hole is matched to the pipeline of the first exhaust pipe, and the communication hole is concernedwith the communication between the first exhaust pipe and the secondexhaust pipe.

According to the fifth aspect, it is possible to equalize thecross-section of the pipe line of each exhaust pipe over the effectivepipe length matched to each operational range of the engine irrespectiveof the presence of the valve body. Effective exhaust inertia effectand/or exhaust pulsation effect that is matched to each operationalrange may therefore be obtained. In particular, when the valve body iscontrolled at the medium speed control position, it is possible toequalize the cross-section of the pipe line of each exhaust pipe overthe entire length, and hence to significantly obtain the above-describedeffect and improve the medium speed output performance of the engine.

According to a sixth aspect of the present invention, of the firstexhaust pipe and the second exhaust pipe on the downstream side from thevalve housing, only the second exhaust pipe is connected to a primaryexhaust purifying system. The first exhaust pipe and the second exhaustpipe are connected to an exhaust collection pipe on the downstream sidefrom the primary exhaust purifying system. A secondary exhaust purifyingsystem is provided in the exhaust collection pipe.

According to the sixth aspect, in the low speed operational range of theengine, in which the flow rate of exhaust gas is relatively small, thevalve body is controlled at the low speed control position. In thiscase, all of the exhaust gas having passed through the valve housing canbe sequentially introduced to the primary and secondary purifyingsystems, thereby purifying the exhaust gas. The primary exhaustpurifying system can be heated to an activation temperature at an earlystage, and the entire cost of the exhaust purifying systems can bereduced because an exhaust purifying system is not provided on the firstexhaust pipe side. In the medium or high speed operational range of theengine, the valve body is controlled at the medium or high speed controlposition. In this case, the exhaust gas having passed through the firstexhaust pipe does not pass through the primary exhaust purifying system;however, in such a state, the flow rate of the exhaust gas becomesrelatively large and all of the exhaust gas passes through the secondaryexhaust purifying system. Therefore, the purifying function of thesecondary exhaust purifying system is sufficiently enhanced by theexhaust heat of the exhaust gas, and the reaction heat, and thereby allthe exhaust gas can be effectively purified.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a side view of a motorcycle including intake and exhaustcontrol systems according to an embodiment of the present invention;

FIG. 2 is a sectional side view of an intake control system according toan embodiment of the present invention;

FIG. 3 is a view illustrating the function of the intake control systemshown in FIG. 2;

FIG. 4 is a sectional view taken on line 4—4 of FIG. 2;

FIG. 5 is a sectional view taken on line 5—5 of FIG. 4;

FIG. 6 is sectional view taken on line 6—6 of FIG. 4.

FIG. 7 is perspective view of an exhaust system according to anembodiment of the present invention;

FIG. 8 is side view of the exhaust control system;

FIG. 9 is sectional view taken on line 9—9 of FIG. 8, showing an exhaustcontrol valve located at a low speed control position;

FIG. 10 is a sectional view taken on line 10—10 of FIG. 9;

FIG. 11 is a sectional view, similar to FIG. 9, showing the exhaustcontrol valve located at a medium speed control position;

FIG. 12 is a sectional view, similar to FIG. 9, showing the exhaustcontrol valve located at a high speed control position;

FIG. 13 is an enlarged plan view showing an exhaust system according tothe present invention;

FIG. 14 is a sectional view taken on line 14—14 of FIG. 13;

FIG. 15 is a sectional view taken on line 15—15 of FIG. 14;

FIG. 16 is a sectional view taken on line 16—16 of FIG. 13;

FIG. 17 is sectional view taken on line 17—17 of FIG. 16;

FIG. 18 is a plan view showing a drive system for driving the intakecontrol valve and the exhaust control valve;

FIG. 19 is a sectional view taken online 19—19 of FIG. 18; and

FIG. 20 is a sectional view taken on line 20—20 of FIG. 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a side view of a motorcycle including intake and exhaustcontrol systems according to an embodiment of the present invention. InFIG. 1, a body frame 2 of a motorcycle 1 includes a pair of right andleft main frames 4 which have a head pipe 3 at the front ends thereof,and are connected to each other at the rear ends thereof. Seat rails 5are connected to the rear ends of the main frames 4 and extendrearwardly and upwardly therefrom. A parallel four-cylinder engine En ismounted on the pair of main frames 4 in so that a cylinder block 8 and acylinder head 9 are tilted slightly forwardly and the cylinder head 9 isinserted between the main frames 4.

A front fork 6 f for rotatably supporting a front wheel 7 f is steerablyconnected to the head pipe 3. A rear fork 6 r for supporting a rearwheel 7 r is vertically swingably connected, via a pivot 11, to a rearportion of a crank case 10 of the engine En, and a rear cushion 12 isinterposed between the rear fork 6 r and the main frames 4. The rearwheel 7 r is driven via a chain transmission system 14 by an outputshaft 13, disposed in front of the pivot 11, of the engine En.

A fuel tank 15 is mounted on the main frames 4, and a tandem main seat16 is mounted on the seat rails 5.

An intake system In of the engine En including an air cleaner 17 andthrottle bodies 18 is disposed over the cylinder head 9 so as to becovered by the fuel tank 15. An exhaust system Ex of the engine Enincluding exhaust pipes 51 a to 51 d and an exhaust muffler 54 projectsfrom the front surfaces of the cylinder head 9 and the cylinder block 8,passes under the crank case 10, and extends obliquely upwardly.

Referring to FIGS. 1 to 6, the intake system In of the engine En will befirst described.

Referring to FIGS. 1 to 4, four pieces of the throttle valves 18corresponding to four cylinders of the engine En are connected to thecylinder head 9 of the engine En. Air funnels 21 are connected to inletsof intake passages 18 a of the throttle valves 18. A cleaner case 22 ofthe air cleaner 17 is mounted to the four throttle valves 18 so as tohouse all of the air funnels 21. The cleaner case 22 includes a lowercase half 22 b fixed to the throttle valves 18, and a upper case half 22a separably connected to the lower case half 22 b with a small screw 27.An element mounting plate 25 for partitioning the inside of the cleanercase 22 into a lower side non-clean chamber 23 and an upper side cleanchamber 24 is held between both the case halves 22 a and 22 b. A cleanerelement 26 is mounted in a mounting hole 25 a provided in the elementmounting plate 25.

An air inlet 28 through which the non-clean chamber 23 is opened toatmospheric air is provided in one side surface of the lower case half22 b. The air funnels 21 pass through a bottom wall of the lower casehalf 22 b, and inlets of the air funnels 21 are opened to the cleanchamber 24. Accordingly, during operation of the engine En, air havingflowed in the non-clean chamber 23 from the air inlet 28 is filtered bythe cleaner element 26, and is supplied in the clean chamber 24. The airsupplied in the cleaner chamber 24 flows in the throttle bodies 18through the air funnels 21. In each of the throttle bodies 18, the flowrate of the air is adjusted by a throttle valve 29. The air whose flowrate has been adjusted by each throttle body 18 is then sucked in theengine En. At this time, fuel is injected from a fuel injection valve 32mounted on one side wall of each throttle body 18 into an intake port ofthe engine En.

Valve shafts 29 a of the throttle valves 29 provided in the fourthrottle bodies 18 are interlocked with each other, and are operated toopen/close the throttle valves 29 by a throttle grip additionallyprovided on a steering handlebar of the motorcycle 1 via a pulley 30fixed on the outermost valve shaft 29 a and an operating wire 31 woundaround the pulley 30.

A partition wall 34 for partitioning an intermediate portion of thenon-clean chamber 23 into a lower small cross-section passage 33 a andan upper large cross-section passage 33 b is integrally provided on theinner side of the lower case half 22 b, and an intake control valve 35for opening/closing the large cross-section passage 33 b is rotatablysupported by the partition wall 34.

The intake control valve 35 includes a valve plate 36 and a valve shaft37 integrally provided on one end of the valve plate 36. One bearing 38for rotatably supporting one end portion of the valve shaft 37 and apair of right and left bearings 39 for rotatably supporting the otherend portion of the valve shaft 37 are provided on the partition wall 34.

The intake control valve 35 is turned between a first intake controlposition A (see FIG. 2) and a second intake control position B (see FIG.3). At the first intake control position A, the tip of the valve plate36 is brought into contact with a ceiling surface of the largecross-section passage 33 b to fully close the large cross-sectionpassage 33 b. At the second intake control position B, the valve plate36 is thrown down in parallel to the partition wall 34 to fully open thelarge cross-section passage 33 b. In the example of the intake controlvalve 35 shown in the figures, the turning angle of the intake controlvalve 35 between the first and second intake control positions A and Bis set at approximately 45 degrees. Additionally, at the second intakecontrol position B of the intake control valve 35, the valve plate 36 istilted with its tip directed to the upstream side of the largecross-section passage 33 b, and the intake negative pressure of theengine En acts to bias the valve plate 36 in the closing direction.

An arm 40 is integrally formed on one end portion of the valve shaft 37.A return spring 41 for biasing the valve plate 36 in the closingdirection, that is, on the first intake control position A side via thearm 40, is connected to the arm 40. A driven pulley 46 is rotatablymounted on the other end portion of the valve shaft 37 at a positionbetween the pair of bearings 39. The driven pulley 46 is connected to adrive pulley 73 of an actuator 71 (which will be described later) via afirst transmission wire 75 a. A lost motion mechanism 42 for connectingthe driven pulley 46 and the valve shaft 37 to each other is providedbetween the driven pulley 46 and the valve shaft 37. The lost motionmechanism 42 includes a transmission pin 43 projecting from one sidesurface of the valve shaft 37, a circular-arc groove 44 formed in theinner peripheral surface of the driven pulley 46 and extending in thecircumferential direction to be engaged with the transmission pin 43,and a lost motion spring 45 for biasing the driven pulley 46 on thefirst intake control position A side of the intake control valve 35.

The center angle of the circular-arc groove 44 is set to be larger thanthe opening/closing angle of the intake control valve 35. Specifically,when the driven pulley 46 is turned from the retreated position in thedirection of opening the intake control valve 35, that is, on the secondintake control position B side, one end surface of the circular-arcgroove 44 is brought into contact with the transmission pin 43 after itis turned by a specific play angle α, to move the intake control valve35 on the second intake control position B side.

Next, the exhaust system Ex of the engine En will be described in detailwith reference to FIG. 1 and FIGS. 7 to 17.

Referring first to FIGS. 1 and 7, the parallel four cylinders 50 a to 50d of the engine En are arranged in this order from the left side of thevehicle, and ignition of each cylinder is performed in the order of thefirst, second, fourth, and third cylinders 50 a, 50 b, 50 d and 50 c.The first to fourth exhaust pipes 51 a to 51 d corresponding to thefirst to fourth cylinders 50 a to 50 d are connected to the frontsurface of the cylinder head 9. These exhaust pipes 51 a to 51 d extenddownwardly along the front surface of the engine E and curve rearwardlyunder the engine En. The first and fourth exhaust pipes 51 a and 51 dare, under the engine En, adjacently disposed in the lateral direction,and the second and third exhaust pipes 51 b and 51 c are, directly underthe first and fourth exhaust pipes 51 a and 51 d, adjacent to oneanother. An exhaust control valve 55 is provided at intermediateportions of these exhaust pipes 51 a and 51 d.

Referring to FIGS. 8 to 12, the exhaust control valve 55 includes acommon valve housing 56 interposed in the intermediate portions of thefirst to fourth exhaust pipes 51 a to 51 d, and a valve body 57 mountedin the valve housing 56. The upstream sides and the downstream sides ofthe first to fourth exhaust pipes 51 a and 51 d are connected to a frontflange 56A and a rear flange 56B formed at both ends of the valvehousing 56 in the longitudinal direction, respectively. The valvehousing 56 has a pair of inlet ports 56 a opened to the end surface ofthe front flange 56A and matched to the upstream pipe lines of the firstand fourth exhaust pipes 51 a and 51 d and a pair of outlet ports 56 bopened to the end surface of the rear flange 56B and matched to thedownstream pipe lines of the first and fourth exhaust pipes 51 a and 51d. The valve housing 56 also has a cylindrical valve chamber 56 cinterposed between the inlet ports 56 a and the outlet ports 56 b andextending in the direction perpendicular to the axial lines of theseports, and a pair of communication ports 56 d formed between the frontand rear flanges 56A and 56B and matched to the upstream pipe lines andthe downstream pipe lines of the second and third exhaust pipes 51 b and51 c. A pair of communication holes 56 e for communicating thecommunication ports 56 d to the valve chamber 56 c are provided on theupper side of the communication ports 56 d.

One end of the valve chamber 56 c is blocked with an end wall integratedwith the valve housing 56, and a bearing bush 59 is mounted in the endwall. The other end of the valve chamber 56 c is opened and closed witha bearing bracket 58 fixed to the valve housing 56 with a bolt 64. Thebearing bracket 58 includes a bearing bush 60 disposed coaxially withthe bearing bush 59.

The valve body 57 is rotatably mounted in the valve chamber 56 c. Thevalve body 57 has a generally cylindrical shape. Valve shafts 61 and 62are integrally formed on both ends of the valve body 57 in the axialdirection, and are rotatably supported by the bearing bushes 59 and 60,respectively. The valve shafts 61 and 62 are turned between a low speedcontrol position C, a medium speed control position D, and a high speedcontrol position E.

The bearing bush 60 of the bearing bracket 58 projects slightly from theinner end surface of the bearing bracket 58 for supporting the endsurface of the valve body 57. The bearing bush 60 is made from anonmetal material excellent in not only bearing characteristic but alsosealing characteristic. The bearing bush may be made from, for example,carbon graphite.

A driven pulley 67 is fixed to the tip portion, projecting outwardlyfrom the bearing bracket 58, of the valve shaft 62 with a nut 65. Thedriven pulley 67 is driven via second and third transmission wires 75 band 75 c by the drive pulley 73 of the actuator 71.

A flange portion 80 having an annular holding recess 80 a opened to thebearing bracket 58 side is integrally formed on the driven pulley 67. Anannular retainer 81 and two thrust washers 82 and 82′ relativelyrotatably held in the retainer 81 are housed in the holding recess 80 a.A thrust spring 83 is provided between the thrust washers 82 and 82′ andthe bearing bracket 58 so as to be contracted by a specific load,whereby the end surface of the valve body 57 is pressed to the endsurface of the bearing bush 60 in a sealing state. In this state, a gap“g” is formed between the end wall, opposed to the bearing bracket 58,of the valve housing 56 and the opposed end surface of the valve body57. The gap “g” is formed to allow for thermal expansion of the valvebody 57 in the axial direction.

The valve body 57 has a pair of through-holes 57 a crossing the axialline of the valve body 57 and being allowed to be matched to the inletports 56 a and the outlet ports 56 b, and communication holes 57 b foropening one-sided surfaces of the through-holes 57 a in the radialdirection of the valve body 57.

At the low speed control position C of the valve body 57 (see FIGS. 9and 10), the communication holes 57 b are matched to the inlet ports 56a of the valve housing 56, the one-end sides of the through-holes 57 aare matched to the communication holes 56 e of the valve housing 56, andthe outlet ports 56 b are closed with valve walls 57A, opposed to thecommunication holes 57 b, of the valve body 57.

At the medium speed control position D (see FIG. 11), the through-holes57 a are matched to the inlet and outlet ports 56 a and 56 b, and thecommunication holes 56 e are closed with the valve walls 57A. The outersurface of the valve wall 57A has a circular arc recess 57 c which iscontinuous to the inner peripheral surface of the communication port 56d at the medium speed control position D (see FIG. 11).

At the high speed control position E (see FIG. 13), the through-holes 57a are matched to the inlet and outlet ports 56 a and 56 b, and thecommunication holes 57 b are matched to the communication holes 56 e.Accordingly, the medium speed control position D and the high speedcontrol position E of the valve body 57 are separated from each other byabout 180 degrees, and the low speed control position C is present at anintermediate point therebetween.

Referring to FIGS. 1, 7 and 13, on the downstream side from the exhaustcontrol valve 55 located at the intermediate portions of the first tofourth exhaust pipes 51 a to 51 d, the first and fourth exhaust pipes 51a and 51 d are connected to an upper first exhaust collection pipe 52 afor collecting the first and fourth exhaust pipes 51 a and 51 d, and thesecond and third exhaust pipes 51 b and 51 c are connected to a lowerfirst exhaust collection pipe 52 b for collecting the second and thirdexhaust pipes 51 b and 51 c. The exhaust collection pipes 52 a and 52 bare connected to a second exhaust collection pipe 53 for collecting theexhaust collection pipes 52 a and 52 b, and the exhaust muffler 54 isconnected to the rear end of the second exhaust collection pipe 53. Ofthe upper and lower first exhaust collection pipes 52 a and 52 b, onlythe lower first exhaust collection pipe 52 b connected to thecommunication ports 56 d of the exhaust control valve 55 is providedwith a primary exhaust purifying system 84, and the second exhaustcollection pipe 53 is provided with a secondary exhaust purifying system85.

The type of the primary exhaust purifying system 84 is not particularlylimited, but according to this embodiment, the primary exhaust purifyingsystem 84 is configured as a three way catalytic converter as shown inFIGS. 14 and 15, which includes a circular catalyst support 87 having alarge number of through-holes 88 formed in its peripheral wall. To bemore specific, the catalyst support 87 is held in the lower firstexhaust collection pipe 52 b so that one end portion is welded to theinner wall of the lower first exhaust collection pipe 52 b, and theother end portion is slidably held by the same inner wall via a heatinsulation member 89 made from glass wool, steel wool, or the like, anda cylindrical heat insulation space 90 is provided between anintermediate portion of the catalyst support 87 excluding both the endsand the lower first exhaust collection pipe 52 b. Accordingly, thermalextension of the primary exhaust purifying system 84 is permitted by asliding motion of the primary exhaust purifying system 84 against theheat insulation member 89, so that it is possible to suppress occurrenceof thermal strain of the primary exhaust purifying system 84 and thelower first exhaust collection pipe 52 b. By the presence of the heatinsulation member 89 and the heat insulation space 90, it is possible tothermally insulate the primary exhaust purifying system 84 and toprevent the over-heating of the lower first exhaust collection pipe 52b.

Referring to FIGS. 16 and 17, the second exhaust collection pipe 53includes an outer pipe 92 extending on the upstream side, and an innerpipe 93 extending on the downstream side. The inner pipe 93 is disposedin the outer pipe 92 with a cylindrical heat insulation space 94 puttherebetween. The downstream end of the outer pipe 92 is welded to theouter periphery of the inner pipe 93, and the upstream end of the innerpipe 93 is relatively slidably supported by the outer pipe 92 via a heatinsulation member 95 made from glass wool, steel wool, or the like. Anintermediate portion of the second exhaust collection pipe 53 isslightly bent, and at the bent portion, a guide ring 96 surrounding theinner pipe 93 is welded to the inner peripheral surface of the outerpipe 92.

The type of the secondary exhaust purifying system 85 is notparticularly limited, but according to this embodiment, the secondaryexhaust purifying system 85 is configured as a three way catalyticconverter as shown in FIGS. 16 and 17, which includes a circularcatalyst support 98 having a large number of through-holes 99 formed inits peripheral wall. The catalyst support 98 is mounted, at its axialcentral portion, to the inner pipe 93 via a heat insulation member 100and a retainer ring 101. The heat insulation member 100 is made fromglass wool, steel wool, or the like. The retainer ring 101 is formed byoverlapping and welding end portions, opposed to each other, of a pairof semi-annular bodies 101 a and 101 b to each other. Upon formation ofthe retainer ring 101 by welding the semi-annular bodies 101 a and 101 bto each other, a compression force is given to the heat insulationmember 100 to impart a frictional force, which is required for slidablyretaining the catalyst support 98, between the heat insulation member100 and the catalyst support 98. The inner pipe 93 has a pair ofprojections 93 a projecting radially inwardly and opposed to each otherin the diameter direction. The outer peripheral surface of the retainerring 101 is welded to the projections 93 a, and a heat insulation space102 is provided between the retainer ring 101 and the inner pipe 93while excluding the welded portion. A portion, other than the centralportion retained by the retainer ring 101, of the catalyst support 98 issufficiently separated from the inner peripheral surface of the innerpipe 93 for allowing exhaust gas to flow in or out of the catalystsupport 98 through the large number of through-holes 99.

Since the secondary exhaust purifying system 85 is slidably retained, atits central portion, by the inner pipe 93 via the heat insulation member100 and the retainer ring 101, the thermal extension of the secondaryexhaust purifying system 85 is permitted by a sliding motion of thesecondary exhaust purifying system 85 against the heat insulation member100, so that it is possible to suppress occurrence of the thermal strainof the secondary exhaust purifying system 85 and the inner pipe 93. Bythe presence of the heat insulation member 100, heat insulation space102, inner pipe 93, and heat insulation space 94 located outside theinner pipe 93, it is possible to reserve the heat of the secondaryexhaust purifying system 85 and to prevent the over-heating of the outerpipe 92. Since the secondary exhaust purifying system 85 is stablyretained at one retaining portion and exhaust gas is allowed to flow inor out of the catalyst support 98 through the through-holes 88 at theportion other than the retaining portion, it is possible to effectivelypurify the exhaust gas. The difference in thermal extension between theouter pipe 92 and the inner pipe 93 constituting the secondary exhaustcollection pipe 53 is permitted by a sliding motion between the innerpipe 93, heat insulation member 95, and outer pipe 92. By the presenceof the double heat insulation spaces 94 and 102 between the secondaryexhaust purifying system 85 and the outer pipe 92, it is possible toeffectively prevent the thermal deterioration of the secondary exhaustpurifying system 85.

Next, a drive system for driving the intake control valve 35 and theexhaust control valve 55 will be described with reference to FIG. 1 andFIGS. 18 to 20.

Referring to FIGS. 1 and 18, a pair of brackets 70 are fixed on theinner surface of the main frame 4 at a position over the crank case 10of the engine En, and the common actuator 71 is mounted via an elasticmember 77 to the brackets 70 with a bolt 78. In this case, the actuator71 is disposed such that a distance between the intake control valve 35and the same is nearly equal to a distance between the exhaust controlvalve 55 and the same. According to the embodiment, as shown in FIG. 18,the actuator 71 is configured as a forward/reverse rotatable electricmotor. The drive pulley 73 fixed to the output shaft 72 of the motor hasa small-diameter first wire groove 73 a, and large-diameter second andthird transmission wire grooves 73 b and 73 c. A first transmission wire75 a is engaged in both the first wire groove 73 a and a wire groove 46aof the driven pulley 46 (see FIG. 6) on the intake control valve 35side, and both terminals of the wire 75 a are connected to the drivepulley 73 and the driven pulley 46. The second and third transmissionwires 75 b and 75 c are respectively engaged in the second and thirdwire grooves 73 b and 73 c and a pair of wire grooves 67 b and 67 c ofthe driven pulley 67 (see FIG. 9) on the exhaust control valve 55 side.In this case, the winding direction of the second transmission wire 75 bis opposed to that of the third transmission wire 75 c. Both terminalsof each of the second and third transmission wires 75 b and 75 c areconnected to the drive pulley 73 and the driven pulley 67.

An electronic control unit 76 connected to the actuator 71 decides a lowspeed rotational range, a medium speed rotational range, and a highspeed rotational range of the engine En on the basis of the speed of theengine En, boosted negative pressure, and the like inputted from sensors(not shown), and controls the actuator 71 in accordance with the decidedrotational range. In this way, as shown in FIG. 20, the actuator 71holds the drive pulley 73 at an initial position “a” in the medium speedrotational range of the engine En; drives the drive pulley 73 from theinitial position “a” to a first drive position “b” separated therefromin the reversal rotation direction R by a specific angle in the lowspeed rotational range; and drives the drive pulley 73 from the firstdrive position “b” to a second drive position “c” separated therefromwhile passing through the initial position “a” in the normal rotationdirection F by a specific angle in the high speed rotational range.

The function of this embodiment will be described below.

When the drive pulley 73 is driven to the first drive position “b” bythe actuator 71 in the low speed rotational range of the engine En, thedrive pulley 73 pulls the first and second transmission wires 75 a and75 b to turn the driven pulley 46 on the intake control valve 35 side inthe valve opening direction (counterclockwise in FIG. 6) by a specificangle, and to turn the driven pulley 67 on the exhaust control valve 35side counterclockwise in FIG. 8 by a specific angle for moving the valvebody 57 of the exhaust control valve 35 to the low speed controlposition C shown in FIGS. 9 and 10.

The rotation of the driven pulley 46 by the specific angle, however, isperformed within the range of the play angle α between the drive pulley73 and the intake control valve 35 in the lost motion mechanism 42, andaccordingly, the valve plate 36 of the intake control valve 35 is heldat the first intake control position A by the biasing force of thereturn spring 41.

In such a state of the intake control valve 35, as shown in FIG. 2, thelarge cross-section passage 33 b is fully closed with the valve plate36, so that air sucked in the engine En passes through the air cleaner17 through the small cross-section passage 33 a Accordingly, even uponaccelerating operation (rapid opening of the throttle valve 29) in thelow speed rotational range, it is possible to supply a suitable richair-fuel mixture to the engine En while suppressing the leaning of theair-fuel mixture, and hence to achieve a good accelerating performance.

When the valve body 57 of the exhaust control valve 55 is moved to thelow speed control position C shown in FIGS. 9 and 10, as describedabove, the communication holes 57 b of the valve body 57 are matched tothe inlet ports 56 a of the valve housing 56 and the one-end sides ofthe through-holes 57 a of the valve body 57 are matched to thecommunication holes 56 e of the valve housing 56, and the output ports56 b are closed with the valve walls 57A of the valve body 57.Accordingly, exhaust gases having flowed from the upstream sides of thefirst and second exhaust pipes 51 a and 51 b into the valve chamber 56 cthrough the inlet ports 56 a of the valve housing 56 collide against thevalve walls 57A of the valve body 57 to be curved to the communicationport 56 d side, and are joined to exhaust gases having passed thecommunication ports 56 d from the upstream sides of the second and thirdexhaust pipes 51 b and 51 c. As a result, the exhaust resistance isincreased, to apply an exhaust pressure suitable for the low speedrotational range from the exhaust pipes 51 a to 51 d to the engine En,thereby improving the low speed output performance by suppressing theblow-by of a new air from the cylinders 50 a to 50 d into the exhaustsystem during the valve overlapping period.

The exhaust gases having passed through the communication ports 56 d ofthe valve housing 56 collectively flow in the lower first exhaustcollection pipe 52 b by way of the downstream sides of the second andthird exhaust pipes 51 b and 51 c, and the joined exhaust gas ispurified by the primary exhaust purifying system 84. Accordingly, theexhaust gases generated by the engine En all flow in the primary exhaustpurifying system 84, and since the primary exhaust purifying system 84is thermally insulated as described above, the primary exhaust purifyingsystem 84 can be early activated, even directly after start-up of theengine En, by the exhaust heat and reaction heat. The exhaust gas havingpassed through the lower first exhaust collection pipe 52 b is fed tothe second exhaust collection pipe 53, and is further purified by thesecondary exhaust purifying system 85. Since the secondary exhaustpurifying system 85 is also thermally insulated as described above, itis possible to promote activation of the secondary exhaust purifyingsystem 85.

In this way, in the low speed rotational range of the engine En, sinceall of the exhaust gases generated from the engine En are purified bythe primary and secondary exhaust purifying systems 84 and 85, it ispossible to enhance the purifying efficiency of the exhaust gas even ifthe temperature of the exhaust gas is relatively low.

During the above-described step, the downstream sides of the first andfourth exhaust pipes 51 a and 51 d are closed with the valve walls 57Aof the valve body 57 to block the flow of the exhaust gases to the upperfirst exhaust collection pipe 52 a, and accordingly, it is not requiredto provide any exhaust purifying system to the upper first exhaustcollection pipe 52 a.

When the rotational state of the engine En is shifted to the mediumspeed rotational range and the drive pulley 73 is returned to theinitial position “a” by the actuator 71, the drive pulley 73 loosens thefirst transmission wire 75 a and pulls the third transmission wire 75 c.The loosening of the first transmission wire 75 a allows the drivenpulley 46 on the intake control valve 35 side to be only returned to theinitial position shown in FIG. 6 within the range of the play angle a bythe biasing force of the lost motion spring 45. At this time, thereoccurs no change of the intake control valve 35 located at the firstintake control position A.

On the other hand, the driven pulley 67 on the exhaust control valve 55side is turned by pulling the third transmission wire 75 c, to move thevalve body 57 to the medium speed control position D shown in FIG. 9. Asa result, as described above, the through-holes 57 a of the valve body57 are matched to the inlet and outlet ports 56 a and 56 b of the valvehousing 56 and the communication holes 56 e are closed with the valvewalls 57A, so that the first to fourth exhaust pipes 51 a to 51 dindividually allow exhaust gases to pass therethrough. In particular,since the through-holes 57 a of the valve body 57 are matched to thepipe lines of the first and fourth exhaust pipes 51 a and 51 d via theinlet and outlet ports 56 a and 56 b, it is possible to equalize thecross-section of the pipe line of each of the first and fourth exhaustpipes 51 a and 51 d over the entire length. Further, since circular-arcrecesses 57 c formed in the outer surfaces of the valve walls 57A of thevalve body 57 so as to face to the communication holes 56 e of the valvehousing 56 are continuous to the inner peripheral surfaces of thecommunication ports 56 d matched to the pipe lines of the second andthird exhaust pipes 51 b and 51 c, it is possible to equalize thecross-section of the pipe line of each of the second and third exhaustpipes 51 b and 51 c over the entire length. Accordingly, each of thefirst to fourth exhaust pipes 51 a to 51 d achieves an effective exhaustinertia effect and/or an effective exhaust pulsation effect by makinguse of the equalized cross-section thereof over the entire length. To bemore specific, the effective pipe length of each of the exhaust pipes 51a to 51 d becomes the maximum length extending from the engine En to theupper and lower first exhaust collection pipes 52 a and 52 b. Themaximum effective pipe length is set such that the exhaust inertiaeffect and/or the exhaust pulsation effect due to the maximum pipelength enhance the volume efficiency of the engine En in the mediumspeed rotational range. As a result, it is possible to enhance themedium speed output performance of the engine En.

When the rotational state of the engine En is shifted to the high speedrotational range and the drive pulley 73 is driven to the second driveposition “c” by the actuator 71, the drive pulley 73 exerts a large pullon the first and second transmission wires 75 a and 75 b. The large pullof the first transmission wire 75 a turns the driven pulley 46 on theintake control valve 35 side in the valve opening direction over theplay angle α, to bring the one end wall of the circular-arc groove 44into contact with the transmission pin 44 of the intake control valve35, thereby moving the valve plate 36 of the intake control valve 35 tothe second intake control position B shown in FIG. 3.

The large pull of the second transmission wire 75 b turns the drivenpulley 67 on the exhaust control valve 55 side by about 180 degrees,thereby shifting the valve body 57 from the medium control position D tothe high speed control position E shown in FIG. 12, while passingthrough the low speed control position C.

When the valve plate 36 of the intake control valve 35 reaches thesecond intake control position B, as shown in FIG. 3, the valve plate 36fully opens the large cross-section passage 33 b, with a result that airsucked in the engine En can pass through both the large cross-sectionpassage 33 b and the small cross-section passage 33 a of the air cleaner17. Accordingly, it is possible to reduce the intake resistance, andhence to enhance the volume efficiency of the engine En and improve thehigh speed output performance.

When the valve body 57 of the exhaust control valve 55 reaches the highspeed control position E, as described above, the through-holes 57 a ofthe valve body 57 are matched to the inlet and outlet ports 56 a and 56b of the valve housing 56 and the communication holes 57 b of the valvebody 57 are matched to the communication holes 56 e of the valve housing56, and accordingly, the exhaust gas passing states of the first tofourth exhaust pipes 51 a to 51 d are not changed. However, theintermediate portions of the first and fourth exhaust pipes 51 a and 51d are communicated to the communication holes 56 e and the intermediateportions of the second and third exhaust pipes 51 b and 51 c arecommunicated to the communication holes 57 b. As a result, the effectivelength of each of the exhaust pipes 51 a to 51 d becomes the minimumlength extending from the engine En to the exhaust control valve 55. Theminimum effective pipe length is set such that the exhaust inertiaeffect and/or the exhaust pulsation effect due to the minimum pipelength enhance the volume efficiency of the engine En in the high speedrotational range. As a result, it is possible to enhance the high speedoutput performance of the engine En.

In the medium or high speed rotational range of the engine En, theexhaust gases having passed through the first and fourth exhaust pipes51 a and 51 d are joined to each other at the upper first exhaustcollection pipe 52 a, and the joined exhaust gas flows to the secondexhaust collection pipe 53, while the exhaust gases having passedthrough the second and third exhaust pipes 51 b and 51 c are joined toeach other at the lower first exhaust collection pipe 52 b and purifiedby the primary exhaust purifying system 84, and the joined and purifiedexhaust gas flows to the second exhaust collection pipe 53; and all theexhaust gases joined to each other at the second exhaust collection pipe53 are purified by the secondary exhaust purifying system 85.Accordingly, the exhaust gases having passed through the first andfourth exhaust pipes 51 a and 51 d are purified only by the secondaryexhaust purifying system 85.

The above-described flow pattern is efficient because the flow rate ofthe exhaust gases becomes relatively large in the medium or high speedoperational range, so that the purifying function of the secondaryexhaust purifying system 85 is sufficiently enhanced by the exhaust heatand reaction heat due to the large amount of the exhaust gases, with theresult that all of the exhaust gases are effectively purified.

In this way, the functions matched to the operational state of theengine En are given to the intake system In and the exhaust system Ex,and accordingly, the output performance of the engine En can beeffectively enhanced in accordance with the low speed rotational range,medium speed rotational range, and high speed rotational range.

In the case where the drive pulley 73 is returned again from the seconddrive position “c” to the first drive position “b” by the actuator 71,when the exhaust control valve 35 is shifted from the high speed controlposition E to the low speed control position C located at theintermediate point, the driven pulley 46 and the valve plate 36 of theintake control valve 35 are returned to the first intake controlposition A shown in FIG. 2 by the lost motion spring 45 and the returnspring 41, and then the driven pulley 46 can be continuously turnedwithin the range of the play angle α of the lost motion mechanism 42. Asa result, the exhaust control valve 35 can be turned, after passingthrough the low speed control position C, to the medium speed controlposition D.

In this way, even if there is a large difference between the rotationalangles of the intake control valve 35 and the exhaust control valve 55,the difference can be absorbed by the lost motion mechanism 42, with aresult that both the control valves 35 and 55 can be accurately operatedby the common actuator 71. In particular, the turning of the drivepulley 73 for operating the exhaust control valve 35 between the lowspeed control position C and the medium speed control position D isabsorbed by the lost motion mechanism 42 and thereby it does not exertadverse effect on the intake control valve 35 located at the firstintake control position A. As a result, the valve body 57 of the exhaustcontrol valve 35 can be freely operated between the low speed controlposition C, medium speed control position D, and high speed controlposition E. In this way, since the actuator 71 is used commonly betweenboth the control valves 35 and 55, it is possible to simplify theconfiguration of the drive system for driving both the control valves 35and 55, and hence to improve the engine performance while reducing thecost of the drive system and further reduce the weight of the drivesystem.

As described above, the bearing bush 60, on the driven pulley 67 side,of the valve housing 56 of the exhaust control valve 55 not onlysupports one valve shaft 62 of the valve body 57, but also receives oneend surface of the valve body 57 biased to the bearing bush 60 side dueto a load applied to the thrust spring 83. In other words, the bearingbush 60 is pressed to the one end surface of the valve body 57 in asealing state, so that the contact area between valve body 57 and thebearing bush 60 can be sealed to thereby prevent the leakage of theexhaust gas from the bearing bush 60 side, without use of any specialseal member. The elimination of the need of provision of any seal memberis effective to reduce the number of parts and to reduce the cost. Inparticular, the use of the bearing bush 60 made from a nonmetal materialsuch as carbon graphite makes it possible to ensure a desirable sealingperformance, and to suppress the occurrence of noise by absorbingvibration of the valve body 57 occurring in the thrust direction due toexhaust pulsation.

The present invention is not limited to the above-described embodiment,and it is to be understood that various changes in design may be madewithout departing from the scope of the present invention. For example,the intake control valve 35 may be configured such that the effectivepipe length of the intake system In is variable depending on theoperational state of the engine En. The present invention can be appliedto a two-cylinder engine, wherein two exhaust pipes of the engine can becontrolled by the exhaust control valve 55 like the first and fourthexhaust pipes 51 a and 51 d and the second and third exhaust pipes 51 band 51 c. The present invention can be also applied to othermulti-cylinder engines.

As described above, according to a first aspect of the presentinvention, there is provided intake and exhaust control systems for anengine, characterized in that an intake control valve for changing anintake mode in accordance with an operational state of an engine isprovided in an intake system of the engine and an exhaust control valvefor changing an exhaust mode in accordance with an operational state ofthe engine is provided in an exhaust system of the engine; and theintake control valve and the exhaust control valve are driven by acommon actuator. Accordingly, it is possible to effectively obtain adesired output performance of the engine irrespective of a change inoperational state of the engine by operating the intake control valveand the exhaust control valve in accordance with the operational stateof the engine by the actuator. Further, since the intake control valveand the exhaust control valve are driven by the common single actuator,it is possible to simplify the configuration of the drive system andhence to improve the engine performance and reduce the cost of the drivesystem, and also to reduce the weight of the drive system.

According to the second aspect of the present invention, the intakecontrol valve is operated between a first intake control position atwhich the intake control valve gives a low speed side compatiblefunction to the intake system and a second intake control position atwhich the intake control valve gives a high speed side compatiblefunction to the intake system; and the exhaust control valve is operatedbetween a first exhaust control position at which the exhaust controlvalve gives a low speed side compatible function to the exhaust systemand a second exhaust control position at which the exhaust control valvegives a high speed side compatible function to the exhaust system.Accordingly, it is possible to enhance the output performance in a wideoperational region of the engine from the low speed operational range tothe high speed rotational range by operation of the intake control valvebetween the first and second intake control positions, and operation ofthe exhaust control valve between the first and second exhaust controlpositions.

According to the third aspect of the present invention, a lost motionmechanism for absorbing a difference in operational amount between theintake control valve and the exhaust control valve is provided betweenthe actuator and the intake control valve or between the actuator andthe exhaust control valve, and accordingly, even if there is a largedifference between the operational amounts of the intake control valveand the exhaust control valve, both the control valves can be operatedby the common actuator.

According to the fourth aspect of the present invention, an exhaustcontrol system includes an exhaust control valve, the exhaust controlvalve including a common valve housing interposed on the way of a firstexhaust pipe and a second exhaust pipe connected to cylinders differentin ignition timing and a valve body mounted in the valve housing andswitchably turned between a low speed control position, a medium speedcontrol position, and a high speed control position, wherein at the lowspeed control position of the valve body, the first exhaust pipe iscommunicated to the second exhaust pipe and the first exhaust pipe isclosed on the downstream side of the communicated portion; at the mediumspeed control position, the first exhaust pipe and the second exhaustpipe individually allow exhaust gases to pass therethrough; and at thehigh speed control position, the first exhaust pipe and the secondexhaust pipe individually allow exhaust gases to pass therethrough, andan intermediate portion of the first exhaust pipe is communicated to anintermediate portion of the second exhaust pipe. Accordingly, the outputperformance in each operational range can be improved by controlling thevalve body at the low speed, medium speed, or high speed controlposition in accordance with the low speed, medium speed, or high speedoperational range of the engine, thereby increasing the back pressure ofthe engine or changing the effective pipe length of each exhaust pipe.

According to the fifth aspect of the present invention, the valve bodyis supported in the valve housing so as to be turned between the lowspeed control position, the medium speed control position, and the highspeed control position, and the valve body has a through-hole crossingthe axial line of the valve body and a communication hole for openingone side surface of the through-hole in the radial direction of thevalve body; and at the low speed control position of the valve body, thecommunication hole and the through-hole are concerned with the mutualcommunication of the first exhaust pipe and the second exhaust pipe, anda valve wall, opposed to the communication hole, of the valve body isconcerned with the closing of the downstream side of the first exhaustpipe; at the medium control position, the through-hole is matched to thepipe line of the first exhaust pipe, and the valve wall is concernedwith the blocking between the first exhaust pipe and the second exhaustpipe; and at the high speed control position, the through-hole ismatched to the pipe line of the first exhaust pipe, and thecommunication hole is concerned to the communication between the firstexhaust pipe and the second exhaust pipe. Accordingly, it is possible toequalize the cross-section of the pipe line of each exhaust pipe overthe effective pipe length matched to each operational range of theengine irrespective of the presence of the valve body, and hence toobtain effective exhaust inertia effect and/or exhaust pulsation effectmatched to each operational range. In particular, when the valve body iscontrolled at the medium speed control position, it is possible toequalize the cross-section of the pipe line of each exhaust pipe overthe entire length, and hence to significantly obtain the above-describedeffect and improve the medium speed output performance of the engine.

According to the sixth aspect of the present invention, of the firstexhaust pipe and the second exhaust pipe on the downstream side from thevalve housing, only the second exhaust pipe is connected to a primaryexhaust purifying system; the first exhaust pipe and the second exhaustpipe are connected to an exhaust collection pipe on the downstream sidefrom the primary exhaust purifying system; and a secondary exhaustpurifying system is provided in the exhaust collection pipe.Accordingly, in the low speed operational range of the engine in whichthe flow rate of exhaust gas is relatively small, the valve body iscontrolled at the low speed control position. In this case, all of theexhaust gas having passed through the valve housing can be sequentiallyintroduced to the primary and secondary purifying systems, to therebypurify the exhaust gas; the primary exhaust purifying system can beheated to an activation temperature at an early stage; and the entirecost of the exhaust purifying systems can be reduced because any exhaustpurifying system is not provided on the first exhaust pipe side.Further, in the medium or high speed operational range of the engine,the valve body is controlled at the medium or high speed controlposition. In this case, the exhaust gas having passed through the firstexhaust pipe does not pass through the primary exhaust purifying system;however, in such a state, the flow rate of the exhaust gas becomesrelatively large and all of the amount of the exhaust gas passes throughthe secondary exhaust purifying system, so that the purifying functionof the secondary exhaust purifying system is sufficiently enhanced bythe exhaust heat of the large amount of the exhaust gas and the reactionheat and thereby all of the exhaust gas can be effectively purified.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed:
 1. A control system for controlling an intake and anexhaust of an engine, the control system comprising: an intake controlvalve for changing an intake mode of the engine in accordance with anoperational state of the engine, said intake control valve is located inan intake manifold upstream of a throttle valve; an exhaust controlvalve for changing an exhaust mode of the engine in accordance with anoperational state of the engine, said exhaust control valve is locatedin an exhaust manifold; and an actuator, the actuator operatablyconnected to actuate both the intake control valve and the exhaustcontrol valve.
 2. The control system of claim 1, wherein the intakecontrol valve is operable at: a first intake control position, the firstintake control position facilitating operation of the engine when theengine operates at a first speed; and a second intake control position,the second intake control position facilitating operation of the enginewhen the engine operates at a second speed higher than the first speed.3. The control system of claim 2, wherein the exhaust control valve isoperable at: a first exhaust control position, the first exhaust controlposition facilitating operation of the engine when the engine operatesat a first speed; and a second exhaust control position, the secondexhaust control position facilitating operation of the engine when theengine operates at a second speed higher than the first speed.
 4. Thecontrol system of claim 1, wherein the actuator is operable to impartdiffering degrees of motion on the intake control valve and the exhaustcontrol valve, the actuator including a compensating device for allowingthe actuator to exert the differing degrees of motion.
 5. The controlsystem of claim 4, wherein the compensating device is a lost motiondevice.
 6. The control system of claim 4, wherein the compensatingdevice is disposed either between the actuator and the intake controlvalve, or between the actuator and the exhaust control valve.
 7. Thecontrol system of claim 2, wherein the intake control valve includes avalve plate pivotable about a valve shaft, the valve plate allowing alarger volume of air to pass through an air cleaner element when theintake control valve is at the second intake control position.
 8. Thecontrol system of claim 1, wherein the actuator is operably connected tothe intake control valve by a first cable, and operably connected to theexhaust control valve by at least a second cable.
 9. The control systemof claim 1, further comprising an electronic control unit forselectively operating the actuator.